An organic electroluminescent device is a device which spontaneously emits light, and the principle of light emission thereof is as follows. When charges are injected into an organic layer between a hole injection electrode and an electron injection electrode, electrons and holes encounter, combined, and then annihilated, and thus light is generated. Organic electroluminescent devices have the characteristics of low voltage, high brightness, wide view angle, or the like. Therefore, organic electroluminescent devices have been rapidly developed in recent years. Among these, the red organic electroluminescent devices have become hot spots of investigation due to the wide prospect for application in terms of monochromatic display, white light modulation, or the like.
Trivalent iridium complexes are considered as ideal organic electroluminescent materials in both the academic world and the industrial world all the time due to the advantages of high light-emitting effectiveness, adjustable color of light emission, or the like.
A number of domestic and foreign research teams have intended to improve the overall properties of the red organic electroluminescent devices by starting with aspects of material synthesis and device optimization so as to meet the requirement for industrialization. For Example, an organic electroluminescent device was prepared by a doping method using an iridium complex btp2Ir (acac) having standard red emission as a light-emitting material by S. R. Forrest et al., at Princeton University, United States, in 2001. Although this device shows a highly ideal red emission, unbalanced injection of carriers leads to relatively low efficiency and brightness of the device, and the operating voltage of the device is relatively high.
In order to solve these problems, an iridium complex (fbi)2Ir(acac) having a high efficiency was selected as a red dye and was incorporated into a preferred host material to prepare a red organic electroluminescent device having a multilayer structure by Dongge Ma et al., at Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, in 2009. This device has relatively high maximal light-emitting effectiveness and maximal brightness, but the light-emitting effectiveness of the device rapidly attenuates as the current density increases. Furthermore, the complicated structure of the device not only leads to a relatively high cost of production, but is also disadvantageous to the reduction of the operating voltage of the device. A red platinum complex was synthesized as a light-emitting material and a device structure comprising two light-emitting layers were designed and optimized by Zhiming Zhi et al., at The University of Hong Kong, in 2013, and an organic electroluminescent device having a purely red emission was obtained. The efficiency attenuation of this device has been greatly alleviated, but the device still has the problems of relatively high operating voltage and relatively low brightness. As thus can be seen, the overall properties, such as light-emitting effectiveness, brightness, spectral stability, service life, and the like, of the red organic electroluminescent device are still not effectively improved.